Specifically, though not exclusively, the invention is usefully applied in dental aspirating apparatus.
In the following description and in the accompanying figures reference is made to an aspirator (a suction or xe2x80x9cvacuumxe2x80x9d pump) but all of the description could also be applied to compressors.
Aspirators are much-used in dental aspiration plants where a depression has to be created in connection with suction tubes.
It is well-known that the coils of electric motors actuating the aspirators are subject to heating-up: this heating-up increases as the current supply absorbed by the motor increases, which in turn increases in line with the degree of depression required.
To limit this heating-up, a valve is usually provided, usually arranged in the aspiration conduit connecting the aspirator to the environment in which the depression is to be created. When the valve is opened it places the aspiration conduit (or the above-mentioned environment) in connection with the outside. This valve is opened when a predetermined pressure difference is reached between the outside environment and the inside environment, which corresponds to a predetermined electrical current which crosses the motor coils. In this way, without stopping the machine, excessive heating-up is avoided due to over-heating of the motor coils.
The problems encountered with compressors when the internal pressure increases are very similar.
The heat produced by aspirators is dispersed in the outside environment. For this reason the manufacturers always recommend that the machines be located in well-aired and cool places in order for the machine to perform optimally. Unfortunately, for reasons of space, aesthetic preference, or in order to avoid any irritation that might be caused by the admittedly low noise level of aspirators, these machines are often arranged in small and closed places, generally lacking in air; sometimes they are even kept away from the outside environment.
In these conditions, the heat dispersed by the aspirators causes considerable build-up of heat in the surrounding atmosphere, with a consequent heating of the aspirator to beyond realistic limits, causing deterioration in its performance or even faulty functioning and, in particularly grave cases, or in the absence of devices blocking the motor when it reaches dangerous temperatures, a fire hazard. All of the above can happen without the electric current in the coils reaching levels which correspond to a depression level warranting the interjection of the above-cited valve, which would reduce electric current absorption and thus reduce the heat produced by the machine.
If there is a thermal cut-off protection for the motor, a frequent case, the motor is shut down before the aspirator reaches its maximum potential. To prevent machine shut-down, or to reduce its occurrence to an absolute minimum, sometimes the manufacturers themselves calibrate the pressure-differential valves to more prudent levels, thus in effect lowering the potential of the machine and doing an injustice to those users who carefully follow the instructions provided with the machine and locate the aspirator in a correct ambience in order to allow plenty of ventilation.
The main aim of the present invention is to obviate the above-cited drawback in the prior art, by providing a device for regulation of compressors and aspirators which enables the machines to function at maximum potential when the conditions of the outside environment are optimal, but which reduces the machine""s performance level when there is an imperfect surrounding environment.
A further aim of the invention is to prevent excessive heating-up of the machine without having to shut the machine down.
An advantage of the device is that it can be applied easily to existing machines. These aims and more besides are all attained by the invention as it is characterized in the claims that follow.
In a delivery conduit for a compressor or an aspiration conduit for an aspirator, which connects the compressor or the aspirator to a closed environment, a first valve is inserted, and opening and a closing of which is commanded by a temperature of an external environment. The valve is normally closed for external temperatures which are lower than a predetermined level and open, placing the conduit in communication with the outside environment, when the external temperature exceeds the predetermined level.